This invention relates in general to solenoid valves for electronic brake control systems and in particular to a solenoid valve coil wound upon an integrated bobbin and flux ring assembly.
An Electronic Brake Control System (EBCS) is often included as standard equipment on new vehicles. When actuated, the EBCS is operative to modulate the pressure applied to the vehicle wheel brakes. A typical EBCS includes a plurality of solenoid valves mounted within a control valve body and connected to the vehicle hydraulic brake system between the brake master cylinder and the individual wheel brake cylinders. The solenoid valves usually are normally open, or isolation, valves and normally closed, or dump, valves. Proportional solenoid valves also can be included. The valve body further includes one or more accumulators for the temporary storage of brake fluid during an operating cycle of the EBCS.
A separate hydraulic source, such as a motor driven pump, is usually included in the EBCS. The pump supplies pressurized brake fluid for reapplying the controlled wheel brakes during an EBCS operational cycle. The pump is typically included within the control valve body while the pump motor is mounted upon the exterior of the control valve body. The pump motor is usually a direct current motor which operates from the vehicle power supply. Typically, the motor runs continuously during an EBCS braking cycle.
An EBCS further includes an electronic control module which has a microprocessor. The microprocessor is electrically connected to the pump motor, a plurality of solenoid coils associated with the solenoid valves, and wheel speed sensors for monitoring the speed and deceleration of the vehicle wheels. The microprocessor also is typically electrically connected to the brake light switch and receives a signal from the switch when the vehicle brakes are applied. Additionally, the EBCS may include one or more accelerometers which also are connected to the microprocessor. The microprocessor includes a memory portion which stores control algorithms for each mode of operation of the EBCS. The control algorithms comprise a set of instructions for the microprocessor which control the operation of the EBCS. The control module is usually mounted upon the valve body. The assembled valve body, motor and control module form a compact unit which is often referred to as an electro-hydraulic control unit.
During vehicle operation, the microprocessor in the EBCS control module continuously receives speed signals from the wheel speed sensors. Depending upon the received signals, the microprocessor can select one of several modes for operation of the EBCS. For example, if the microprocessor detects a potential wheel lock-up condition while the vehicle brakes are applied, the microprocessor will select an Anti-Lock Brake System (ABS) mode of operation and activate an ABS braking cycle. During an ABS braking cycle, the microprocessor actuates the pump motor and selectively operates the solenoid valves in the control valve to cyclically relieve and reapply hydraulic pressure to the wheel brakes. The hydraulic pressure applied to the wheel brakes is adjusted by the operation of the solenoid valves to limit wheel slippage to a safe level while continuing to produce adequate brake torque to decelerate the vehicle as desired by the vehicle operator.
Another mode of operation provides Traction Control (TC). If the microprocessors detect excessive slip of a driven wheel when the wheel brakes are not applied, the EBCS will apply the brakes to the slipping wheel and thereby transfer more engine torque to the non-slipping wheel.
The EBCS can also include Vehicle Stability Control (VSC) mode of operation. The VSC mode is entered when the microprocessor detects a potential loss of directional control, such as, for example, a spin-out of the vehicle. In the VSC mode of operation, selected wheel brakes are applied to restore directional control of the vehicle.
Referring now to FIG. 1, there is shown a partial sectional view of a typical EBCS solenoid valve 10 mounted upon an EBCS control valve body 11. The control valve body includes a plurality of internal passages (not shown) that communicate with the valve 10. The valve 10 is a digital valve, that is, it is either open or closed. The particular valve 10 shown in FIG. 1 is a normally open valve, however, the following discussion also applies to normally closed valves. The valve 10 includes an axially shiftable armature (not shown) which is biased in an upward direction by a spring (not shown) such that a ball valve (not shown) is maintained in a normally open position. The ball valve cooperates with a valve seat member 15 which is mounted in the valve body 11. The armature and ball valve are slideably disposed within a valve sleeve 16 having a closed end.
A solenoid coil 20 is carried by the valve sleeve 16 and surrounds the armature 12. The coil 20 is enclosed by a cup shaped metal flux casing 21. The valve sleeve 16 extends through an aperture 22 formed in the upper end of the flux casing 21. An annular flux ring 23 is disposed in the open lower end of the flux casing 21. The flux casing 21 and flux ring 23 complete a magnetic flux path which passes through the armature and the valve seat member 15.
The solenoid coil 20 is of conventional design, comprising a winding 24 formed from multiple turns of an insulated magnet wire having a round cross section, such as #28 xc2xd magnet wire. The magnet wire is helically wound upon a plastic bobbin 26. The bobbin 26 has a cylindrical center portion 28 that terminates in upper and lower flanges, 30 and 32, respectively. A pair of terminal pin supports 34 extend in an axial direction from the top of the bobbin 26. Each of the supports 34 is molded over a terminal pin 36. An end 38 of the coil winding wire is wound around the base of each of the terminal pins 36 and soldered thereto. The pins 36 are electrically coupled to via a printed circuit board (not shown) to the EBCS microprocessor.
When it is necessary to actuate the valve 10 during an anti-lock braking cycle, an electric current is supplied through the terminal pins 36 to the solenoid coil 20. The current establishes a magnetic field in the armature which pulls the armature in a downward direction, closing the ball valve. When the current is interrupted, the magnetic field collapses, allowing the spring to return the armature to its original position, thereby reopening the ball valve. An EBCS control unit also typically includes other digital solenoid valves, such as normally closed solenoid valves (not shown), which have structures similar to the normally open valve 10 described above. Additionally, an EBCS control unit can include proportional solenoid valves.
This invention relates to a solenoid valve coil wound upon an integrated bobbin and flux ring assembly.
For electronic brake control systems being currently developed, vehicular solenoid valves can be energized for long periods of time. The energized coils generate heat that must be conducted away from the coils to avoid overheating. Conventional coil bobbins typically have air gaps and low-pressure contacts between the bobbins and the metal parts of the other components of the control system. Accordingly, current units have poor heat conduction properties. Therefore, a coil assembly having improved heat conduction properties would be desirable.
The present invention contemplates a bobbin assembly for a solenoid valve coil that includes a bobbin formed from an electrically insulative material with a bore extending axially therethrough. The bobbin assembly further includes a flux ring formed from a magnetically permeable material having a high heat conductivity. The flux ring has an annular base portion and a tubular sleeve extending axially into an end of the bobbin bore. The bobbin has a pair of flanges formed upon the ends thereof. A winding is wound upon the bobbin between said flanges.
The bobbin assembly can include a second flux ring that also is formed from a magnetically permeable material having a high heat conductivity. The second flux ring has an annular base portion and a tubular sleeve extending into an end of the bobbin bore opposite from the other flux ring.
The bobbin can include an annular ring formed upon an inner surface of the bore and spaced from the ends of the bore. The annular ring forms a stepped bore within the sleeve with the steps positioning at least one of the first and second flux rings within the bore. Alternately, the bobbin can include an least one axially extending rib formed upon an inner surface of the bore and spaced from the ends of the bore. The rib positions at least one of the first and second flux rings within the bore.
The invention further contemplates that the coil and flux rings are received within a flux casing with at least one of the flux rings secured to the flux casing. In the preferred embodiment, the flux rings are pressed into the ends of the flux casing to retain the coil and flux rings within the flux casing.
The invention also contemplates a method for fabricating a solenoid coil assembly that includes forming a bobbin having a generally tubular shape with an axial bore extending therethrough. A flux ring having a sleeve portion extending axially from an annular base portion is provided and the sleeve portion of the flux ring is pressed into an end of the bobbin bore. A coil is then wound upon the bobbin to form a coil assembly. The coil assembly is inserted into a flux casing and the flux casing is secured to the coil assembly. The invention further contemplates that the step of mounting a flux ring upon the bobbin center portion also can include providing a second flux ring having a sleeve portion extending axially from an annular base portion and pressing the sleeve portion of the flux ring into the end of the bobbin bore that is opposite from the first flux ring.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.